1. Field of the Invention
The present invention relates to a bearing structure for a rotatable shaft having an end rotatably supported by a side wall.
2. Description of the Related Art
It is known to provide a radiation image recording and reproducing system for recording radiation image information of a subject, such as a human body, using a stimulable phosphor, and either reproducing the recorded radiation image information on a photosensitive medium such as a photographic film or the like or displaying the recorded radiation image information on a cathoderay tube or other display units.
When a radiation energy such as X-rays, .alpha.-rays, .gamma.-rays, electron beams, ultraviolet radiation, or the like is applied to a certain phosphor, it stores part of the applied radiation energy. When stimulating light such as visible light is subsequently applied to the phosphor, the phosphor emits light depending the stored radiation energy. Such a phosphor is referred to as a stimulable phosphor. A stimulable phosphor is usually used in the form of a sheet which is referred to as a stimulable phosphor sheet.
The radiation image recording and reproducing system includes an image information reading apparatus comprising a reading unit for reading image information recorded on a stimulable phosphor sheet and an erasing unit for erasing remaining image information from the stimulable phosphor sheet after the recorded image information has been read therefrom by the reading unit. The image information reading apparatus has a cassette loading section for receiving therein a cassette which stores a stimulable phosphor sheet on which radiation image information of a subject has been recorded by an external exposure unit.
After the cassette is inserted into the cassette loading section, the lid of the cassette is opened, and the stimulable phosphor sheet is removed from the cassette by a sheet feeding mechanism. The removed stimulable phosphor sheet is then delivered to the reading unit by a sheet delivering mechanism. The reading unit reads the radiation image information from the stimulable phosphor sheet by applying stimulating light to the stimulable phosphor sheet. Thereafter, the stimulable phosphor sheet is delivered to the erasing unit, which erases remaining image information from the stimulable phosphor sheet. The stimulable phosphor sheet is then delivered back and inserted into the cassette in the cassette loading section.
The radiation image recording and reproducing system also includes an image information reproducing apparatus comprising a recording unit for recording radiation image information on a photosensitive medium. The image information reproducing apparatus carries a magazine which stores a plurality of photosensitive mediums. One, at a time, of the photosensitive mediums is removed from the magazine, and delivered to the recording unit by a sheet delivering mechanism. The recording unit records the radiation image information read from a stimulable phosphor sheet on the photosensitive medium by scanning the photosensitive medium with a laser beam that has been modulated by the radiation image information.
Both the image information reading apparatus and the image information reproducing apparatus have a number of roller pairs each comprising a pair of rollers held in rolling contact with each other, for delivering a stimulable phosphor sheet or a photosensitive medium (hereinafter also referred to as a "sheet"). Specifically, one of the rollers of each roller pair comprises a drive roller which is driven to rotate about its own axis and the other roller comprises a nip roller which can move into and out of rolling contact with the drive roller. The drive roller and the nip roller grip a sheet therebetween and deliver the sheet upon rotation of the drive roller.
Roller pairs are employed in the sheet delivering mechanisms for delivering sheets to the reading unit and the recording unit, and also in auxiliary scanning mechanisms for feeding sheets in an auxiliary scanning direction in the reading unit and the recording unit. Usually, such a roller pair extends between and is rotatably mounted on side walls. To install each of the rollers of the roller pair, plain bearings or ball bearings are attached to respective opposite ends of the shaft of the roller, and then E-rings are attached to the ends of the shaft to retain the plain bearings or the ball bearings in position against unwanted movement on the shaft in the axial direction.
However, since E-rings cannot easily be attached and removed, using them is detrimental to the efficiency with which to assemble and service the rollers and the bearings. Particularly in cases where many roller pairs are employed, the processes of assembling and servicing the rollers and the bearings are considerably tedious and time-consuming.
E-rings may be dispensed with if snap-fitting gears, directly mounted on the shaft, are used to prevent the plain bearings or the ball bearings from axially moving on the shaft. The snap-fitting gears have fingers therein which snap in corresponding recesses defined in the shaft when the snap-fitting gears are installed on the shaft. While the shaft is rotating, thrust-induced stresses are applied to the fingers, which are subjected to relatively large thrust forces acting on the shaft. Consequently, the fingers tend to become damaged quickly, and the snap-fitting gears are poor in durability.